Learning Elixir: Guess a number between a given range

chop.exs

defmodule Chop do
  def guess(actual, range = low..high) when actual >= low and actual <= high do
    _guess(actual, ask(div(low + high, 2)), range)
  end


  defp _guess(actual, actual, _) do
    IO.puts "\nYES! It is #{actual}\n"
  end

  defp _guess(actual, answer, (_..high)) when answer < actual do
    guess(actual, (answer + 1..high))
  end

  defp _guess(actual, answer, (low.._)) when answer > actual do
    guess(actual, (low..answer - 1))
  end

  defp ask(answer) do
    IO.puts "Is it #{answer}?"
    answer
  end
end